1. Field of the Invention
The present invention relates to a sliding constant-velocity joint used for a driving-force transmission path in a vehicle and the like.
2. Description of Related Art
A conventional sliding constant-velocity joint is described, for example, in Japanese Patent Application Publication No. 2012-197803 (JP 2012-197803 A). The sliding constant-velocity joint includes an outer ring shaped like a bottomed tube and having three raceway grooves, a tripod member with three tripod shaft portions extending in a radial direction, and double-roller-type roller units respectively supported by the tripod shaft portions so as to be pivotal. Each of the double-roller-type roller units has an outer roller that can roll through the corresponding raceway groove in the outer ring, an inner roller pivotally supported on an outer peripheral surface of the corresponding tripod shaft portion, and a plurality of rolling members (needle rollers) interposed between the outer roller and the roller so as to be able to roll. The tripod shaft portion is arranged so as to be able to swing with respect to the roller unit.
In the sliding constant-velocity joint described in JP 2012-197803 A, when a shaft fitted in the tripod member is tilted and rotated with respect to the outer ring, the roller unit is tilted in the raceway groove (pitching) to cause the outer roller and a ceiling surface of the raceway groove (a bottom surface of the raceway groove on the outer peripheral side in the outer ring) slide on each other. Thus, sliding friction occurs between these sliding portions. Furthermore, the outer roller rolls with an axial direction of the rolling elements tilted with respect to a direction in which the raceway groove extends. Consequently, sliding friction also occurs on an outer peripheral surface of the outer roller. Such sliding friction caused by the tilt of the roller unit is a factor in occurrence of a compelling force (inducing thrust force).